It's unusual for the surface of the tile itself to look the way you describe. All I can think of is that it looked that way already, beneath any soil that was on it, and you just exposed it for what it was. Ceramic tile can lose its shine, but that can take a pretty long time.

Before sealing, you should wait until the grout is fully dry. I have always taken that to mean overnight drying. I have heard that there is a grout sealant that can be applied immediately after cleaning. Maybe you could inquire over at www.dirtygrout.com and see what they say.